1. Field of the Invention
The present invention relates to a projection type liquid crystal display apparatus including a liquid crystal display device incorporated therein. More particularly, the invention relates to a projection type liquid crystal display apparatus including a liquid crystal display device having microlenses formed on a light entering side thereof.
2. Description of the Related Art
Presently, projection type liquid crystal display apparatus including a liquid crystal display device incorporated therein (liquid crystal projectors) are actively developed. Projection type liquid crystal display apparatus are categorized based on their functions and configurations into data projectors to be used with personal computers, front projectors for home theater applications, rear projectors to be used in used in rear projector televisions, and so on.
Projection type liquid crystal display apparatus are broadly classified into single plate type products employing one liquid crystal display device in which sub-pixels rendered in three colors, i.e., red (R), green (G), and blue (B) are provided at each dot and three plate type products employing three monochromatic liquid crystal display devices or one monochromatic liquid crystal display device in each of R, G, and B optical paths. A projection type liquid crystal display apparatus is categorized as a transmission type projector or a reflection type projector depending on whether the liquid crystal display device serving as the core of the product is a transmission type device or a reflection type device.
There are high level requirements for projection type liquid crystal display apparatus in terms of brightness, image quality, definition, and price. Especially, there are strong demands for improvement in the amount of light projected by such displays.
The amount of projected light is an index of the degree of visibility of the image projected, and one factor determining the amount of projected light is the liquid crystal display device used. A liquid crystal display device has the function of spatially modulating light emitted by a light source according to an image signal and outputting a modulated image thus obtained. The light modulated by the liquid crystal display device is projected onto a projection surface such as a screen or wall to form an image on the projection surface.
Such a liquid crystal display device includes thin film transistors (TFTs) and the like fabricated on a substrate to drive pixels, and a light blocking region called a black matrix is provided such that it intervenes between each pair of adjoining pixels. Therefore, no such liquid crystal display device has an aperture ratio of 100%.
Under the circumstance, one approach taken in the related art toward improvement in the effective aperture ratio of a liquid crystal display device is to dispose a microlens in association with each dot (each pixel or sub-pixel) in the direction of the optical axis of the dot, the microlenses being formed on a substrate provided on a light entering side of the device. The effective aperture ratio of a liquid crystal display device is the ratio of total amount of light beams exiting the liquid crystal display device to the total amount of light beams entering the liquid crystal display device. When defining the effective aperture ratio of a projection type liquid crystal display apparatus, attention is paid not only to optical loss at the liquid crystal display device but also to optical vignetting which can occur at a projection lens provided downstream of the device.
When microlenses are disposed on a substrate provided on a light entering side of a liquid crystal display device as thus described, optical loss attributable to the light-blocking effect of a black matrix can be reduced. However, the light exiting the device diverges significantly because of the converging effect of the lenses, which can result in optical vignetting at a projection lens provided downstream of the device. When a projection lens having a small F-number is used, problems such as a cost increase and a reduction in image forming performance can occur.
Under the circumstance, some liquid crystal display devices recently developed include microlenses provided to mitigate the above-described problems in addition to microlenses disposed on a light entering side thereof.
For example, JP-A-6-75212 and JP-A-5-341283 (Patent Documents 1 and 2) disclose liquid crystal display devices having second microlenses for collimating light beams diverged by first microlenses disposed on a light entering side. Such a configuration cancels the divergence of light exiting the devices attributable to the converging effect of the first microlenses. Thus, the divergence of the exiting light is suppressed to achieve a high effective aperture ratio.